A sample pattern inspection apparatus is adapted to illuminate an electron beam(s) on a sample to be inspected such as a wafer to generate electrons having information relating to a device pattern formed on the sample surface, make an image of the device pattern from the generated electrons, and inspect the obtained image on the basis of a predetermined inspection program. High accurate information of the devise pattern of the sample surface is necessary to increase reliability of the inspection result.
However, such a sample pattern inspection apparatus according to a prior art has the following problems.
A stage for loading a sample and moving in X- and Y-directions which are orthogonal to each other, has stage guides for guiding the stage in the X- and Y-directions, respectively. Since the stage guides sometimes have distortion and are not accurately orthogonal to each other, the stage cannot always move through ideal moving paths. Further, a moving velocity of the stage is not always constant during continuous moving. In addition, when a sample is loaded on the stage, the XY coordinate of the sample does not always coincide with the XY coordinate of the stage, resulting in that an error in a rotational direction occurs. In such a case, dies are fabricated on positions which are different from designed positions, during a lithography procedure.
According to the above problems, the sample pattern inspection apparatus cannot always provide accurate results.
When the position errors as above are not compensated, an obtained image may be shifted from an ideal position by ±2 pixels or more, for instance. If the image is shifted from the ideal position by ±2 pixels in both X- and Y-directions, 49 (=7×7) image pieces for comparison are required to ensure accuracy of the inspection result. Therefore, since it is necessary to increase the number of memories and comparison circuits which are provided for inspection, a defect inspection speed is lower than an image capturing speed and hence defect inspection with a high throughput cannot be carried out.
The applicant of the subject application has provided a sample defect inspection apparatus as described in the following patent application official gazette. To inspect patterns of dies which are digestedly arranged on the X-Y plane of the sample, the inspection apparatus is adapted to generate a grid with constant intervals along the X- and Y-axes of an ideal X-Y coordinate on which dies are virtually arranged; obtain actual position coordinate of the respective dies; calculate position errors or displacements between the position of the constant interval grid and the actual position; and compensate the position coordinates of the respective dies on the basis of the position errors so that the dies are arranged along the constant interval grid.
In the compensation of the position coordinate, a compensation XY map is prepared in which the position errors obtained correspondingly to the position coordinates of the constant interval grid, are stored, and in response to a position error stored in the compensation XY map, a voltage which is applied to a compensation electrode located at a front stage of a MCP for instance, is adjusted, so that the electron beam is polarized to match a die position on the wafer to an image position on the MCP.
Prior Art Document 1:
Japanese Patent Application Public Disclosure No. 2000-91342
However, in some cases, the compensation (in the prior art document that the voltage to be supplied to the compensation electrode, is adjusted in response to the position error information in the compensation XY map) is not satisfactory. For instance, in general, static compensation of ±20 μm or more is required, while a polarization dynamic range by a compensation electrode is around ±20 μm, which may not cover the required range.
Further, in the prior compensation, positions of a plurality of points on a wafer are measured, and position errors of the points are obtained, while position errors of points other than the measured points are obtained using an interpolation method. However, the position measurements of the points are not always accurate. Therefore, if a position error of a measured point is abnormal, the results of the interpolation are irrelevant because of the abnormal position error.
The invention has been made in view of the above problems. It is an object of the invention to provide an electron beam apparatus for inspecting sample patterns, which is capable of reducing problems which are caused by stage guide distortion, orthogonal errors of the stage guide and so on, and inspecting with a high accurate and high throughput even if a stage is not located at a predetermined position, dies on a wafer are not located in line with theoretical ideal coordinate and/or a moving speed is not constant.